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ECE 4371, Fall, 2015 Introduction to Telecommunication Engineering/Telecommunication Laboratory Zhu Han Department of Electrical and Computer Engineering Class 3 Sep. 1 st , 2015
ECE 4371, Fall, 2015
Introduction to Telecommunication Engineering/Telecommunication Laboratory
Zhu Han
Department of Electrical and Computer Engineering
Class 3
Sep. 1st, 2015
ReviewReview Double side band and AM modulation
– Time domain equation and figure– Frequency domain equation and figure– Frequency conversion– Modulation index– AM modulation and demodulation– Coherent vs. non-coherent demoludation
QAM and Single side band, Vestigial side band FDM system Analog TV
QAMQAM AM signal BANDWIDTH : AM signal bandwidth is twice the bandwidth
of the modulating signal. A 5kHz signal requires 10kHz bandwidth for AM transmission. If the carrier frequency is 1000 kHz, the AM signal spectrum is in the frequency range of 995kHz to 1005 kHz.
QUADRARTURE AMPLITUDE MODULATION is a scheme that allows two signals to be transmitted over the same frequency range.
Coherent in frequency
and phase. Expensive TV for analog Most modems
Single Sideband (SSB)Single Sideband (SSB)• Purpose : to reduce the bandwidth requirement of AM by one-half. This is achieved by transmitting only the upper sideband or the lower sidebband of the DSB AM signal.
SSB FrequencySSB Frequency
)(M
0 B2B2
cc
SSB (Upper sideband)
0
0cc
)(SSB
baseband
DSB
SSB
SSB MathSSB Math
)(M
)(M
)sgn( )M()(M )}{sgn( H j
)t(jmm(t) t
1)t(jmm(t) )t(m thatshow can weSimilarly,
m(t). of transform Hilbert the called is )t(m
dt
)(m1 t
1)t(m )t(m e wher
)t(jmm(t) t
1)t(jmm(t) )t(m tj
tj
1)}{sgn(
)}{sgn()}(M{m(t))t(m)sgn()(M)(M 2
)sgn(1)(M )(U)(M)(M
h21
21
h
h
h21
211
1121
21
21
1F
F
FF
How to generate mh(t) ?
H()M() Mh()
0 for j 0 for j
)jsgn(- )M()(M )H(
)sgn( )M(j)(M
H
H
1 )H(
) H( 2
2Transfer function of a Hilbert transformer
SSB HilbertSSB Hilbert• SSB signal can be expressed in terms of m(t) and its Hilbert transform
) LSB for USB, for (- )tsin()t(m )tcos( m(t))( general, In
;)tsin()t(m )tcos( m(t))( thatshow can weSimilarly,
)tsin()t(m )tcos( m(t))(
)tsin()t(m )tcos( m(t)
)ee)(t(mj)ee)(t(m
}e))t(jm)t(m(e))t(jm)t(m({ )(M)(M
e))t(jm)t(m({}e)t(m{)(M
}e))t(jm)t(m({}e)t(m{)(M
)(M)(M)(
chcSSB
chcLSBSSB
chcUSBSSB
chc
tjtjh21tjtj
21
tjh21tjh2
1cc
tjh21tjc
tjh21tjc
ccUSBSSB
cccc
cc
cc
cc
1-
1-
1-1-
1-
1-
1-1-
1-1-
F
F
FFF
FFFFF
SSB GeneratorSSB Generator• Selective Filtering using filters with sharp cutoff characteristics. Sharp
cutoff filters are difficult to design. The audio signal spectrum has no dc component, therefore , the spectrum of the modulated audio signal has a null around the carrier frequency. This means a less than perfect filter can do a reasonably good job of filtering the DSB to produce SSB signals.
• Baseband signal must be bandpass
• Filter design challenges
• No low frequency components
cc 0
SSB GeneratorSSB Generator Phase shift method using Hilbert transformer Non-causal filter, approximations
HilbertTransformer
x
X
+
+
m(t)
~2
)cos c )t(ssb
SSB DemodulationSSB Demodulation
).t(m get to used be can filter lowpass A
)t2sin()t(jm))tcos(1)(t(m)t(ncos()tsin()t(jm)tcos()t(m)tcos()t(
21
chc21
cchccSSB
large. be to has A sincelow very is scheme this of efficiency The
.(t)m A ,m(t) A for )t(mA
1 A
))t(Am2)t(m))t(mA(())t(m))t(mA((E(t)
))(tan ),cos(BA)Bsin() Acos(call{Re
?)tcos()t(E)tsin()t(m))tcos())t(mA()t( of envelope the is What. signals SSB such demodulate to used be can detector envelope An
)tsin()t(m)tcos()t(m)tcos(A)t(
h
A)t(m2
A)t(m
A)t(m
2h
222h
2AB1-22
cchcCSSB
chccCSSB
2
2h
2
2
21
21
21
Synchronous, SSB-SC demodulation
SSB+C, envelop detection
SSB vs. AMSSB vs. AM Since the carrier is not transmitted, there is a reduction by 67%
of the transmitted power (-4.7dBm). --In AM @100% modulation: 2/3 of the power is comprised of the carrier; with the remaining (1/3) power in both sidebands.
Because in SSB, only one sideband is transmitted, there is a further reduction by 50% in transmitted power
Finally, because only one sideband is received, the receiver's needed bandwidth is reduced by one half--thus effectively reducing the required power by the transmitter another 50%
(-4.7dBm (+) -3dBm (+) -3dBm = -10.7dBm). Relative expensive receiver
Vestigial Sideband (VSB)Vestigial Sideband (VSB)• VSB is a compromise between DSB and SSB. To produce SSB signal from
DSB signal ideal filters should be used to split the spectrum in the middle so that the bandwidth of bandpass signal is reduced by one half. In VSB system one sideband and a vestige of other sideband are transmitted together. The resulting signal has a bandwidth > the bandwidth of the modulating (baseband) signal but < the DSB signal bandwidth.
cc
SSB (Upper sideband)
0
0cc
)(SSB
VSB Spectrum
c
)(VSB
c
DSB
Filtering scheme for the generation of VSB modulated wave.Filtering scheme for the generation of VSB modulated wave.
VSB TransceiverVSB Transceiver
)t2cos( c
Hi()
m(t) )(VSB
)t2cos( c
LPFHo()
)(M )(VSB
Transmitter Receiver
e(t)
)(H)(H
1)(H OR
B2 for 1)(H)(H)(H have should weThusthis. removes filter Lowpass
)(H)]2(M)(H)2(M)(H[ )(H)(M)(H)(H)(H)(E)(M
term freq. High term freq. High
])2(M)(H)(M)(H)(M)(H)2(M)(H[ )]()([)(E
)(H)](M)(M[)( rad/sec B2 to dbandlimite is )(M
cicio
ocici
occicci
ocicio
ccicicicci
cVSBcVSB
iccVSB
Other Facts about VSBOther Facts about VSB Envelope detection of VSB+C Analog TV: DSB, SSB and VSB
– DSB bandwidth too high – SSB: baseband has low
frequency component, receiver cost
– Relax the filter and basebandrequirement with modest increasein bandwidth
((aa) Idealized magnitude ) Idealized magnitude spectrum of a transmitted TV spectrum of a transmitted TV
signal. (signal. (bb) Magnitude ) Magnitude response of VSB shaping response of VSB shaping
filter in the receiver.filter in the receiver.
ComparisonComparison
AM
DSB
QAM 1 2
Common types & modulated signal 1. AM: ( ) [1 ( )]cos(2 ) 2. DSB: ( ) ( ) cos(2 ) 3. QAM: ( ) ( )cos(2 ) ( )sin(2 )
4. SSB:
c c
c c
c c c c
s t A m t f ts t A m t f ts t A m t f t A m t f t
SSB
VSB
2
ˆ ( ) ( ) cos(2 ) ( )sin(2 ) 5. VSB: ( ) ( ) cos(2 ) ( )sin(2 ) Complex domain representation:
( ) Re{ ( ) }, complex envelop:
c
c c c c
c c c c
j f t
s t A m t f t A m t f ts t A m t f t A m t f t
s t g t e
( ) ? Bandwidth: 2 ( : message bandwdith)m m m
g tB B B B
Block diagram of FDM system.Block diagram of FDM system.
Illustrating the modulation steps in an FDM systemIllustrating the modulation steps in an FDM system
FMA of SSB for FMA of SSB for Telephone Systems Telephone Systems
FMA of SSB for FMA of SSB for Telephone Systems Telephone Systems
FMA of SSB for FMA of SSB for Telephone Systems Telephone Systems
AM BroadcastingAM Broadcasting History Frequency
– Long wave: 153-270kHz– Medium wave: 520-1,710kHz, AM radio– Short wave: 2,300-26,100kHz, long distance, SSB, VOA
Limitation– Susceptibility to atmospheric interference– Lower-fidelity sound, news and talk radio– Better at night, ionosphere.
Superheterodyne vs. homodyneSuperheterodyne vs. homodyne Move all frequencies of different channels to one medium freq.
– In AM receivers, that frequency is 455 kHz, – for FM receivers, it is usually 10.7 MHz.
– Filter Design Concern– Accommodate more radio stations– Edwin Howard Armstrong
TelevisionTelevisionDigital Display (CRT)Analog Display (TV)
Eliminate flicker effects
Deflection Signal and SynchronizationDeflection Signal and Synchronization
525525 30=8.27M
Deflection signal and synchronization signal
Solar Power and Human EyeSolar Power and Human Eye
RGB, LIQRGB, LIQ
mL=0.3mr+0.59mg+0.11mb
mI=0.6mr+0.28mg-0.32mb
mQ=0.21mr-0.52mg+0.31mb
NTSC, PAL, and SECAMNTSC, PAL, and SECAM National Television System Committee
– Low complexity, higher vertical color resolution– 525 line/60Hz(30frames per second)
Phase Alternative Line: PAL– The phase of the color components is reversed from line to line– Robust to Multipath, phase distortion– 625line/50Hz(25 frames per second), slightly larger bandwidth
SECAM– Requires the receiver to memorize the content of each line
Mono when used for different standards
TV standards in the worldTV standards in the world
Why is it Changing for Digital TV?Why is it Changing for Digital TV?
No snow, no static, no ghosts Higher resolution images, and Sound Additional channels Frees up Bandwidth for Other Important Needs More Options
– Improved captions (but not without pain)– Interactive TV– TV to your Cell Phone or PDA? (Iphone, Asia)
Digital is Better
ResolutionResolution
Clearer and More Detailed
ATSC
ATSC
Digital TVDigital TV
Signal is just a bunch of bits Define color and intensity of
each point on the screen Bit stream is heavily
compressed Captions are also digital
Displays as Pixels
1010011000101101110100110001011011
And That’s the News, Tonight
SummarySummary Digital TVs Should be Fine
– High Definition Video and Audio– Some Requirements to Get Captions
Learn where captions will be decoded Learn how to control Use the right connectors
– More Options for Captions Color Font size and style Opacity
Analog TVs Will Still Work With Digital/Analog Converter– Cable and Satellite Subscribers (May have to trade in STB)– Cable and Satellite Subscribers may still want a D/A Converter for emergencies– Must Buy Converter Box To View Over The Air Signal on Analog TV
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